Momentary Child is an optional boss, found on the last floor of Marukyu Striptease and appears after the twelfth of July. It does not have to be fought in order to proceed in the storyline, but defeating it will boost the protagonist's Courage and grant access to the Bear Claw weapon for Teddie behind the stage.
Momentary Child is weak to Ice, so bringing Teddie and Chie is recommended. It is a fairly easy boss fight, as he only uses Physical Attacks and the party can have up to three party members able to knock him down. The Shadow will typically spend a turn to cast Tarukaja or Rebellion before attacking. A warning stating "Momentary Child is indignant" will show the turn before it uses Deathbound, so the party may need to guard as necessary. One or two characters with either Diarama or Media may be necessary.